Preprints
https://doi.org/10.5194/egusphere-2022-1440
https://doi.org/10.5194/egusphere-2022-1440
 
21 Dec 2022
21 Dec 2022
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

Elucidating ozone and PM2.5 pollution in Fenwei Plain reveals the co-benefits of controlling precursor gas emissions in winter haze

Chunshui Lin1, Ru-Jin Huang1,2,3,4, Haobin Zhong1,5, Jing Duan1, Zixi Wang3,6, Wei Huang1, and Wei Xu1 Chunshui Lin et al.
  • 1State Key Laboratory of Loess and Quaternary Geology (SKLLQG), Center for Excellence in Quaternary Science and Global Change, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710061, China
  • 2Institute of Global Environmental Change, Xi'an Jiaotong University, Xi'an 710049, China
  • 3University of Chinese Academy of Sciences, Beijing 100049, China
  • 4Laoshan Laboratory, Qingdao 266061, China
  • 5School of Advanced Materials Engineering, Jiaxing Nanhu University, Jiaxing 314001, China
  • 6State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China

Abstract. Fenwei Plain, home to 50 million people in central China, is one of the most polluted regions in China. In 2018, Fenwei Plain is designated as one of the three key regions for the “Blue Sky Protection Campaign”, along with the Beijing-Tianjin-Hebei (BTH) and Yangtze River Delta (YRD) regions. However, compared to BTH and YRD, our understanding of the current status of air pollution in the Fenwei Plain is limited partly due to a lack of detailed analysis of the transformation from precursor gases to secondary products including secondary organic aerosol (SOA) and ozone. Through the analysis of 7 years (2015–2021) of surface monitoring of the air pollutants in Xi’an, the largest city in the Fenwei Plain, we show that roughly 2/3 of the days exceeded either the PM2.5 or the O3 level-1 air quality standard, highlighting the severity of air pollution. Moreover, an increase in O3 pollution in the winter haze was also revealed, due to the constantly elevated reactive oxygenated volatile organic compounds (OVOCs), and in particular formaldehyde with ozone formation potential of over 50 μg m−3 in combination with the reduced NO2. The abrupt decrease of NO2, as observed during the lockdown in 2020, provided real-world evidence of the control measures, targeting only NOx (70 % decrease on average), were insufficient to reduce ozone pollution because reactive OVOCs remained constantly high in a VOC-limited regime. Model simulation results showed that with NO2 reduction from 20–70 %, the self-reaction rate between peroxy radicals, a pathway for SOA formation, was intensified by up to 75 %, while the self-reaction rate was only reduced with a further reduction of VOCs of > 50 %. Therefore, a synergic reduction in PM2.5 and O3 pollution can only be achieved through a more aggressive reduction of their precursor gases. This study elucidates the status of ozone and PM2.5 pollution in one of the most polluted regions in China, revealing a general trend of increasing secondary pollution i.e., ozone and SOA in winter haze. Controlling precursor gas emissions is anticipated to curb both ozone and SOA formation which will benefit not just the Fenwei Plain but also other regions in China.

Chunshui Lin et al.

Status: open (until 10 Feb 2023)

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Chunshui Lin et al.

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Short summary
The complex interaction between O3 and PM2.5, coupled with the topology of the Fenwei Plain and the evolution of the boundary layer height, highlight the challenges in further reducing particulate pollution in winter despite years of efforts to reduce emissions. Through scenario analysis in a chemical box model constrained by observation, we show the co-benefits of reducing NOx and VOCs simultaneously in reducing ozone and SOA.